Photosensitive paper base material and method of making the same



John F. Cipriano, Philadelphia, Research and Manufacturing Pa., :1 firm Pa., assignor to Adelphi Company, Philadelphia,

No Drawing. Application November 25, 1952, Serial No. 322,547

12 Claims. (Cl. 117-34) The present invention relates to a method of preparing paper prior to the application of photosensitive materials in the manufacture of photosensitive paper, and to the resulting product; and, more particularly, the invention relates to the treatment of paper which is to be coated with photosensitive materials in the manufacture of photoprint paper, such as blueprint paper, brownprint paper, diazotype print papers, photographic paper, and the like, and to the resulting treated paper.

In the manufacture of photosensitive papers, such as those enumerated above, a sheet of finishedpaper is coated with a light-sensitive coating. in the manufacture of blue print paper, for example, the paper is coated with a solution containing an iron salt or salts. In printing with the resulting paper, the paper is exposed to light under an opaque design, then the sheet is washed to remove the portions of the coating which are not affected by the light. The portions which have been affected by the light can be converted to a blue color by the use of a suitable developing solution of, for example, potassium dichromate.

Much work has been done in the increase the intensity of the dark areas and thus to increase the contrast between dark and light areas in photoprints. A recent advance in this regard is the method described and claimed in U. S. Patent No. Re. 23,510. The process of this patent involves coating a finished sheet of paper with a layer of discrete submicroscopic particles of silica as by applying to the sheet of an aqueous silica sol, that is, a colloidal dispersion of sub microscopic silica particles in. water, followed by drying. While this treatment has the effect of increasing the contrast between the light and dark portions of the photoprint, the method possesses a substantial limitation in that the coating has to be applied to a finished, calendered sheet of paper. The coating can not be applied to an unfinished sheet of paper before calendering, since calendering destroys the coating. The result of this limitation is that the paper-coaters,- that is, those who coat finished paper with photosensitive maerials, are forced to apply the silica precoating, whereas it would be much more desirable and economical for many reasons if the paper manufacturers themselves could apply the coating, for example, in the conventional surface sizing tub, before the paper is calendered.

A further limitation possessed by all conventional photosensitivepapers, including those treated in accordance with the process of the above-discussed patent, is the tendency for the photosensitive paper to deteriorate upon standing due possibly to the action of the photosensitive chemicals. This seriously reduces storagelife in photosensitive papers. Still another limitation of the process of the above-discussed patent is that because a relatively large amount of silica must be applied to the paper in order to achieve the desired results, the tearing and folding properties of the treated paper are deleteriously affected. Furthermore, the silica particles are highly abrasive and this property has been found to exert undue wear on coating and cutting equipment.

It is the principal object of the present invention to provide a method of treating paper of the type which is to be provided with a light-sensitive coating, as the result of which treatment the final photosensitive paper, upon printing and developing, possesses greater intensity of color and/ or greater contrast between light and dark areas than conventional photoprints.

Another object of the present invention is to provide a method of treating paper of the type which is to be coated with photosensitive material which treatment may be past in an attempt to States Patent thereto as a coating,

accomplished as a step in the manufacture of a paper sheet by the paper manufacturers.

Still another object of the present invention is to provide a sheet of paper which, when coated with photosensitive materials, exposed and developed, will provide a print possessing a more intense color and/ or a greater contrast between light and dark areas than does conventional photosensitive paper.

A further object of the invention is to provide a pretreated paper the treated surface of which is capable of adsorbing a greater quantity of photosensitive chemicals than do conventional photosensitive paper bases.

A further object is to provide a treated which, when the photosensitive materials are applied is not as readily adversely affected upon storage by the photosensitive chemicals as are conventional photosensitive paper bases, and which, therefore, possesses greater storage life.

A further object is to provide a method of of the type described wherein no diminution and folding properties of the sheet results.

treating paper of the tearing Other objects will become apparentfrom a consideration of the following specification and claims.

The process of the present invention comprises coating a sheet of paper with a fluid aqueous dispersion of a basic aluminum sheet. (Herein and in the claims the terms paper sheet and sheet of paper will, unless otherwise qualified, refer to a finished calendered sheet as well as to an unfinished gel; that is, the basic carbonate first formed is kept cool and wet at all times. The gel, in order to be satisfactory from the standpoint of the present invention, must have a relatively high content of CO2, and generally the gel will contain at least about 0.6 mol of CO2 per mol of A1203 and the CO2 content may go up to about 1.6 mol per mol of A1203. Preferably, the gel will contain between about .8 and about 1.2 mol of CO2 per mol of A1203. made up into an aqueous suspension containing the equivalent of about 4% A1203 will have a pH of 6.0-7.5. At a concentration in water above about 6% A1203, the gel has the consistency and appearance of cottage cheese and will exhibit thixotropic properties. Such a gel is hydrophilic and disperses readily in water to form a milky suspension. An example of a gel which is particularly applicable for use in accordance with the present invencontrasted to a sol, a silica sol, which is a colloidal suspension of dehydrated The gel is preferably substantially free of other adverse effect mphotoprmt desired,

may range from as low as about .1% to as high as about sheet of paper carbonate gel and drying the resulting coated The gel when .materials to the paper. For

avire side of the sheet, although least the felt side since sensitizing chemicals are normally applied to this calendered, it may may then be sensitized by coating the treated surface of 4% of AlzOs. Preferably, the concentration of the gel in the suspension applied to the paper is equivalent to between about .5% and about 2%, A1203.

The pH of the suspension as applied to the paper is between about 5.5 and about 7. As pointed out above, the pH of the gel will normally be between about 6 and about 7.5 and thus, in certain cases, no adjustment of the pH thereof may be necessary. If adjustment of the pH of the gel is necessary in order to provide the desired pH, conventional acids or acid salts, alkaline materials, as the case may be, may be added to the gel.

In addition, it may be desirable, if the suspension is to stand for any length of time, to dispersing agent to retard or prevent the settling of the basic aluminum carbonate gel particles. In this connection, a magnesium aluminum silicate sold under the name of Veegum HV by the R. T. Vanderbilt Company has been found to be particularly advantageous. Other materials may be included in the suspension for any reason thatmay be desired. For example, conventional antifeathering agents, such as resins, gums, and the like, may be incorporated in the suspension.

The suspension may be applied to the paper by any one of a wide variety of means, depending in part upon the particular stage in the manufacture of the paper sheet at which the suspension is to be applied. Where the suspension is to be applied to a finished, calendered sheet,

the suspension may be applied by spraying, brushing, by applicator rolls, and the like. .to be applied to the unfinished, uncalendered sheet, in ac- Where the suspension 1s cordance with the preferred embodiment of the present invention, the suspension may be applied by dipping as in the conventional sizing tub or by spraying, brushing, applicator rolls, and the like. In this connection, the suspension may be applied in conjunction with the application of other example, a sheet of unfinished paper coming from the first drier section may be first run through a conventional glue sizing tub following which thewe't sized sheet may be sprayed with formaldehyde either alone or in conjunction with the suspension of the gel. The suspension may be applied to either the felt or it is preferred to coat at side of the sheet. It will be seen from the foregoing, that, depending upon the particular technique employed one or both sides of the sheet may be coated. Following application of the suspension to the paper sheet, the sheet is dried, and, if it has not already been be calendered. The resulting paper the sheet with sensitizing chemicals in the normal manner. On the resulting sheet, the basic aluminum carbonate gel coats the fibers thereof. Because of its gel characteristics, the coating possesses a continuous matte structure ul'lhich fills the voids and coats the fibers of the paper s eet.

The product and method of the present invention possesses many important advantages over prior paper adapted to receive light-sensitive coatings and over the prior method of pretreating such paper referred to above. With respect to the method, one of the primary features thereof is the fact that it may be carried out in the normal equipment conventionally used by paper manufacturers,

and thus the process may be carried out by the paper manufacturer as a step incident to the manufacture of the paper sheet. This relieves the manufacturer of photosensitized paper from the burden of precoating the paper, anddoes not require a separate coating and drying procedure as in the case of silica sol. With respect to the precoated product, it has been found that it results in a higher concentration of photosensitive chemicals being adsorbed on the surface of the paper. This results in a more intense color, particularly in the case of blueprint paper, and also in a greater contrast between light and dark areas in the final developed print. Moreover, it has 7 been found that the coating acts as a buffer which neutralizes acidic photosensitive chemicals which are most often used and which would ordinarily in time cause weakening of the paper. Photosensitive papers made from the treated paper of the present invention, therefore, possess greater shelf-life than do prior photosensitive incorporate therein a regular manner.

In addition, the basic aluminum carbonate material possesses unusually high p1gmenting values so that the light areas of the treated sheet possess increased brightness. Furthermore, since the suspension applied to the paper is relatively dilute, being preferably on the order of about 1% solids, the folding and tearing properties of the paper need not diminish to any substantial extent as is the case when silica sol, which requires substantially higher concentration, is employed. Finally, the dried coating is much less abrasive than the silica coating so that the undue wear of coating and cutting equipment encountered when silica coating is employed is eliminated.

The present invention will be more readily understood from a consideration of the following specific examples which are given for the purpose of illustration and are not intended to limit the scope of the invention in any way:

Example I To 20 gallons of water are added 20 pounds of basic aluminum carbonate gel (1-500 of Reheis Company, Inc., 10% A1203), 6 /2 ounces of concentrated HCl and 8 /2 ounces of magnesium aluminum silicate (Veegum HV). This suspension is applied to 2200 yards of paper. The coated paper is then dried. The treated sheet is then coated with a conventional blueprint sensitizing solution and dried in the conventional manner. Blueprints made from the resulting paper are much brighter than the conventional blueprints, the blue being a deeper blue giving greater contrast between the blue portions and the white lines.

Example II To 50 gallons of water are added 40 pounds of basic aluminum carbonate gel (P-500 of Reheis Company, Inc., 10% A1203), and 2 pounds of magnesium aluminum silicate (Veegum HV). The pH of the suspension is adjusted to 5.5 with citric acid. 17 pound, 50% rag paper, of the type normally used in making blueprint paper, coming from the first drier section of a paper-making machine is first immersed in the conventional glue sizing tub and the excess sizing is squeezed out by rollers. A formaldehyde solution is then applied to the wire side of the sheet. The above-described suspension, containing also formaldehyde, is run on to the felt side of the paper sheet, and excess suspension is squeezed off by means of squeeze rolls. The sheet is dried and calendered in the The treated side of the resulting sheet is then coated in the conventional manner with blueprint sensitizing solution. Blueprints made from the resulting Example 111 The suspension used in Example II, without formalde hyde, is used in this example. 17 pound, 50% rag paper coming from the first drier section of a paper-making machine is immersed in a tub containing the stated suspension so that the suspension is applied to both sides of the sheet. Excess suspension is squeezed off by means of squeeze rolls, and the sheet is then dried and calendered in the usual manner. The felt side of the treated sheet is then coated in the conventional manner with blueprint sensitizing solution.

In this example, wet strength materials are incorporated in the paper stock before the Web, is formed, thus eliminating the need for the glue sizing step.

, Considerable modification is possible in the selection of additives and in the particular techniques employed in carrying out the present process without departing from the scope of the invention.

1 claim:

1. The method of treating paper to improve its proper ties as photosensitive paper base which comprises applying to a sheet of paper a fluid aqueous suspension .of a basic aluminum carbonate gel having a pH between about 5.5 and about 7, which basic aluminum carbonate gel has a C02 content of between about .6 mol and about 1.6 mol of CO2 per mol of A1203, and drying the treated sheet.

2. The method of treating paper to improve its properties as photosensitive paper base which comprises applying to a sheet of paper a fluid aqueous suspension of a basic aluminum carbonate gel having a pH between about 5.5 and about 7, which basic aluminum carbonate gel has a C02 content of between about .6 mol and about 1.6 mol of CO2 per mol of A1203, the concentration of basic aluminum carbonate gel in said suspension being equivalent to between about .1 and about 4% A1203, and drying the treated sheet.

3. The method of claim 2 wherein the concentration of basic aluminum carbonate gel in said suspension is equivalent to between about .5 and about 2% of A1203.

4. In the manufacture of paper adapted for use as a base in the preparation of photosensitive paper, the steps of applying to the sheet of paper a fluid aqueous suspension of a basic aluminum carbonate gel having a pH between about 5.5 and about 7, which basic aluminum carbonate gel has a C02 content of between about .6 mol and about 1.6 mol of CO2 per mol of A1203, drying the treated sheet and calendering the sheet.

5. The method of claim 4 wherein the concentration of basic aluminum carbonate gel in said suspension is equivalent to between about .1 and about 4% of A1203.

6. The method of claim 4 wherein the concentration of basic aluminum carbonate gel in said suspension is equivalent to between about .5 and about 2% of A1203.

7. The method of making a paper base material adapted for use as a paper base in the manufacture of photosensitive paper which comprises applying to a calendered sheet of paper a fluid aqueous suspension of a basic aluminum carbonate gel having a pH between about 5.5 and about 7, which basic aluminum carbonate gel has a C02 content of between about .6 mol and about 1.6 mo. of CO1 per mol of A1203, and drying the treated sheet.

8. The method of claim 7 wherein the concentration of basic aluminum carbonate gel in said suspension is equivalent to between about .1 and about 4% of A1203.

9. The method of claim 7 wherein the concentration of basic aluminum carbonate gel in said suspension is equivalent to between about .5 and about 2% A1203.

10. A material suitable as a base sheet in the manufacture of photosensitive paper comprising a sheet of paper having a dried coating of basic aluminum carbonate gel thereon, and prepared by applying to said sheet of paper a fluid aqueous suspension of a basic aluminum carbonate gel having a pH between about 5.5 and about 7, and the basic aluminum carbonate gel having a C02 content of between about .6 mol and about 1.6 mol of CO2 per mol of A1203, and drying said sheet.

11. The method of treating paper to provide an improved photosensitive sheet which comprises applying to a sheet of paper a fluid aqueous suspension of basic aluminum carbonate gel having a pH between about 5.5 and about 7, which basic aluminum carbonate gel has a C02 content of between about .6 mol and about 1.6 mol of CO2 per mol of A1203, drying the treated sheet, and applying to the dried treated sheet photosensitive chemicals.

12. In the manufacture of photosensitive paper the step comprising applying photosensitive chemicals to a sheet of. paper having a dried coating of basic aluminum carbonate gel thereon and prepared by applying to said sheet of paper a fluid aqueous suspension of a basic aluminum carbonate gel having a pH between about 5.5 and about 7 and a C02 content of between about .6 mol ant agout 1.6 mol of CO2 per mol of A1203 and drying sai s eet.

References Cited in the file of this. patent UNITED STATES PATENTS 147,833 Fell Feb. 24, 1874 2,085,129 Stoervener June 29, 1937 FOREIGN PATENTS 16,358 Great Britain 1893 

11. THE METHOD OF TREATING PAPER TO PROVIDE AN IMPROVED PHOTOSENSITIVE SHEET WHICH COMPRISES APPLYING TO A SHEET OF PAPER A FLUID AQUEOUS SUSPENSION OF BASIC ALUMINUM CARBONATE GEL HAVING A PH BETWEEN ABOUT 5.5 AND ABOUT 7, WHICH BASIC ALUMINUM CARBONATE GEL HAS A CO2 CONTENT OF BETWEEN ABOUT 6 MOL AND ABOUT 1.6 MOL OF CO2 PER MOL OF AL2O3, DRYING THE TREATED SHEET, AND APPLYING TO THE DRIED TREATED SHEET PHOTOSENSITIVE CHEMICALS. 